Magnesium metal has, over the years, been produced by any one of several different methods, as for example an electrolytic extraction process developed in Germany by Aluminum and Magnesium Fabrik; the Elektron process, based on conversion of magnesium oxide with carbon and chlorine; the Murex process using calcium carbide as a reducing agent according to equation: EQU MgO + CaC.sub.2 = Mg + CaO + 2C;
and the Ferrosilicon reduction process of Farben Industrie using calcined dolomite in accordance with the equation: EQU 2(MgO + CaO) + Si = (CaO).sub.2 SiO.sub.2 + 2Mg
For various reasons the thermo-processes have never proved successful on a commercial scale. On the other hand, electrolytic extraction processes are in use commercially wherein the source materials are naturally occurring brines, such as sea water and lake brines which are processed to produce hydrous magnesium chloride. However, before the hydrous magnesium chloride can be used as electrolyte for the electrolytic production of magnesium metal it must be converted to substantially anhydrous magnesium chloride by dehydration which, in the interest of low operating costs must be efficient and relatively inexpensive. Moreover, dehydration of the hydrous magnesium chloride must be carried out in a manner such that the anhydrous magnesium chloride produced will be substantially free of major contaminants such as the oxides of magnesium i.e. MgOHCl or MgO. Of the various methods used for dehydrating hydrous magnesium chloride, spray drying has been most effective in producing an anhydrous MgCl.sub.2 with relatively low amounts of the oxides of magnesium. However, efforts to further dehydrate the spray dried product by fluidizing with dry HCl gas, hereinafter referred to as hydrochlorination, have been generally unsuccessful due to the nature of the spray dried dihydrate which is generally so finely divided and of such a light, fluffy nature that fluidization must be carried out at very low gas velocities and with excessively large equipment. The hydrochlorination of spray dried, partially dehydrated magnesium chloride is thereby made relatively complex and expensive.
Attempts to overcome the difficulties encountered with spray dried, partially dehydrated magnesium chloride are illustrated by U.S. Pat. No. 3,742,100, June 26, 1973 and U.S. Pat. No. 3,760,050, Sept. 18, 1973, wherein molten magnesium chloride hydrate is formed into relatively large granules by prilling the melt from a centrifuge or perforated plate. The prills are relatively large and heavy compared to a spray dried product and hence are more amenable to fluidization. Nevertheless, the cost of prilling the hydrous magnesium chloride is relatively high and hence a distinct disadvantage where operational costs must be kept to a minimum in order to be competitive. Further, U.S. Pat. No. 3,346,333, describes atomizing a concentrated magnesium chloride brine comprising 4.2 to 4.4 moles water/mole of magnesium chloride in a fluidized bed using hydrogen chloride as a fluidizing gas. However, the large quantity of water that must be removed in the fluidized bed requires large amounts of heat which necessitates the use of an expensive heat transfer medium as well as specially built and relatively expensive equipment.
In view of the rising demands for magnesium it is desirable, therefore, to provide a process for producing anhydrous magnesium chloride from naturally occurring brines which process will be adapted not only to commercial production schedules but will be relatively simple and economical to operate, will avoid many of the difficulties encountered in the methods of the prior art and will produce substantially anhydrous magnesium chloride that is to say a magnesium chloride particulate material comprising no more than about 1.0% water and no more than about 0.6% magnesium oxide.